I've been running the 3" system for ~9 months and ~4K miles, so I guess I can drop a review now.
I'll preface this with this: I might have a defective system, I think it has an internal rattle on decel ~1900 RPM. It's very repeatable. It didn't bug me enough to try to diagnose it outside in Michigan winter, but it is something I'll tackle soon. I need to double check all the clamps, make sure nothing is hitting, maybe tap it in a few places, and probably take some videos before contacting them. It has a lifetime warranty, so this will be a good customer service test. Whether this has any impact on drone or sound quality, I have no idea.
I'll also say: exhaust is subjective. What one person likes, another might hate. Here's my background: Mid 40's, married with 2 kids, the ST is my daily driver and the family hauler. I'm also a car guy with a few project cars: 2001 Supercharged M5, 1970 Chevy C10, my wife drives a Golf R (which is why the ST is the family hauler)
My overall review: I love it and hate it.
Pros:
1. It sounds fantastic. I get compliments everywhere I go. I find myself using the remote start to start it just so I can hear it fire up from outside the car.
2. Installation was really easy.
Cons:
1. The exhaust tips stick out too far. Because the larger outside diameter part is so short, I have this funny gap between the tip and the bumper. They're pushed in as far as they'll go. I'll have to cut at least an inch off somewhere, maybe two, to get it to tuck in.
2. It's borderline too loud (for me) in some situations (Awful sound insulation in the ST doesn't help)
Steady state cruising at 45mph: "braaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
Steady state cruising at 70mph: "braaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
You will hear it ALL THE TIME. It's not overbearing or anything, but it's there. Music drowns it out easily, I was expecting my wife to say something, but she's probably used to me having cars with loud exhausts.
Drone:
By definition (a low continuous noise that does not change its note), it drones. I experienced exhaust drone (drone with vibration/resonation) once: Six people in the car, kids in the very back, cruise control set to 40mph and going up a slight incline. Enough to drop the RPM but not downshift. My son loudly said "What is happening to my ears right now?!", followed up with: "Oh yeah, daddy's exhaust"
Does the internal rattle have a hand in that? I don't know but possibly, it's right in the RPM range for it.
Loaded car on the highway and going uphill without a downshift, the exhaust note will deepen, but no resonation.
tldr: 20 year old Me would love this system. Mid-40s family man Me wishes he got the 2.5" system.